Mario & Luigi: Superstar Saga was released in 2003 for the Game Boy Advance, an RPG starring the famous Mario Bros.
In this game, Birdo helped the heroes by disguising herself as Princess Peach when Cackletta and Fawful visited the Mushroom Kingdom. When Cackletta attempted to steal the princess' voice, she got Birdo's instead; then, when the Beanish witch tried to use the "pure" voice to awaken the Beanstar, it went berserk. All of this is not revealed until later in the game, when Toadsworth (who originally came up with the plan) and Peach explained the situation to the Mario Bros. As they spoke, Birdo appeared and started wildly chasing one of Lady Lima's assistants, after winking at them flirtatiously.
Birdo expressing her love for Popple.Some time later, Birdo replaces Bowser as Popple's "Rookie" out of her mad love for the Beanish crook. Oddly, she is now an enemy of the Mario Bros. even though she had been a helper before in the game. Birdo was a powerful opponent, as one of her attacks involves sucking in Mario or Luigi. If Birdo is successful in this, it will not only hurt the unfortunate Mario Brother she sucked up, but will also restore her own HP. The only way to dodge this attack is to hit Birdo with a hammer. She can also throw flaming eggs in a wild, sporadic and put Popple in protective but deadly egg shields. The main difference between Birdo's and Popple's first Rookie's attack patterns, however, is that it won't counterattack the Mario Brothers if they attacked Popple first, making her easier to kill them both. Birdo, however, becomes stronger as she turns red and says "You may have defeated my darling, but that's as far as you go!" (a reference to Birdo's line in Super Mario Advance).
After Popple and Birdo failed in their attempt to destroy the Mario Brothers, Popple blamed it all on Birdo and even went as far as to fire his latest apprentice. Birdo (who was noticeably less obedient than Popple's original Rookie) responded by furiously knocking him away and ending their relationship (which was unrequited by Popple anyway). She then gave a short speech about her new dedication to strive towards super-stardom, expressed her anger at Mario and Luigi, and ran away. Although Cackletta stole Birdo's voice, she is able to speak when Mario and Luigi battle Popple and her. This appears to be an error in the game, but Birdo may have got her voice back after Cackletta used it on the Beanstar.